(a - b)^2 x^2 - 4abx - (a-b)^2
solve for x by factorisation method.
The problem is an old one. You have not copied it correctly. It should be
then it can be factored.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
A number by itself is useful, but it is far more useful to know how accurate or certain that number is.